In order to authenticate Ukuleles actually made in Hawaii from those made on the Mainland pretending to be from Hawaii, Hawaiian Ukulele manufacturers registered this trademark and started putting it on their Ukulele's, either on the back of the headstock or inside the soundhole.

This occurred from about 1915 to 1925 and is often the only mark found on a old Hawaiian Ukulele. This is called the Tabu Stamp It is NOT a makers mark - there was never a brand called Tabu.

Not all Hawaiian made Ukuleles of the time carried it, but any that do carry it were made in Hawaii. The practice of using it also didn't abruptly die out in 1925 so some Ukuleles that carry it may be later than 1925, but by this point it has served its purpose and mainland makers no longer tried to pass their Ukuleles off as Hawaiian made.